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Hyperbaric Oxygen Therapy

Emi Latham, MD, FACEP, Assistant Clinical Professor of Emergency and Hyperbaric Medicine, University of California at San Diego
Marc A Hare, MD, Assistant Clinical Professor of Medicine, Department of Emergency Medicine, University of California San Diego Medical Center; Medical Director, Center for Wound Healing and Hyperbaric Medicine, Paradise Valley Hospital; Michael Neumeister, MD, FRCSC, FACS, Program Director, Assistant Professor, Department of Surgery, Division of Plastic Surgery, Southern Illinois University School of Medicine

Updated: Nov 7, 2008

Introduction

Hyperbaric oxygen therapy (HBOT) is breathing 100% oxygen while under increased atmospheric pressure. HBOT is a treatment that can be traced back to the 1600s. The first well-known chamber was built and run by a British clergyman named Henshaw. He built a structure called the domicilium that was used to treat a multitude of diseases.¹  The chamber was pressurized with air or unpressurized using bellows. The idea of treating patients under increased pressure was continued by the French surgeon Fontaine, who built a pressurized, mobile operating room in 1879.² Dr. Orville Cunningham, a professor of anesthesia, ran what was known as the "SteelBall Hospital." The structure, erected in 1928, was 6 stories high and 64 feet in diameter. The hospital could reach 3 atmospheres of pressure.²  The hospital was closed in 1930 because of the lack of scientific evidence indicating that such treatment alleviated disease. It was deconstructed during World War II for scrap.

The military continued work with hyperbaric oxygen. The work of Paul Bert, who demonstrated the toxic effects of oxygen (producing grand mal seizures), as well as the work of J. Lorrain-Smith, who demonstrated pulmonary oxygen toxicity, were used with Navy divers. Exposure times to oxygen at different depths of water (and, hence, different levels of pressure) were quantified and tested based on time to convulsions.²

Oxygen Chambers

When a patient is given 100% oxygen under pressure, hemoglobin is saturated, but the blood can be hyperoxygenated by dissolving oxygen within the plasma. The patient can be administered systemic oxygen via 2 basic chambers: Type A, multiplace; and Type B, monoplace. Both types can be used for routine wound care, treatment of most dive injuries, and treatment of patients who are ventilated or in critical care.

Multiplace chamber

Multiplace chambers treat multiple patients at the same time, generally with a nurse or another inside observer who monitors the patients and assists with equipment manipulation or emergencies. Patients in a multiplace chamber breathe 100% oxygen via a mask or close-fitting plastic hood. Multiplace chambers can usually be pressurized to the equivalent of about 6 atmospheres of pressure. 

If a different mixture of gas (nitrogen or helium mixture) is desired, the mixture can be given, via the mask, to only the patient, not the employee. All equipment used with patients, such as ventilators and intravenous lines, is put into the chamber with the patient. Since the employee is breathing air during the treatment (not using a mask), his or her nitrogen intake must be monitored, as this presents a risk for problems similar to those sometimes developed by scuba divers (eg, decompression sickness [DCS]).

Rectangular hyperbaric chamber.

Interior of rectangular chamber.

Cylindrical multiplace chamber.

A monoplace chamber compresses one person at a time, usually in a reclining position. The gas used to pressurize the vessel is usually 100% oxygen. Some chambers have masks available to provide an alternate breathing gas (such as air). Employees tend to the patient from outside of the chamber and equipment remains outside the chamber; only certain intravenous lines and ventilation ducts penetrate through the hull. Newer Duoplace chambers can hold 2 people; their operation is similar to that of a monoplace chamber.

Monoplace chamber.

Two other types of chambers are worth mentioning, although they are not considered HBOT.

Topical oxygen, or Topox, is administered through a small chamber that is placed over an extremity and pressurized with oxygen. The patient does not breathe the oxygen, nor is the remainder of the body pressurized. Therefore, the patient cannot benefit from most of the positive effects of HBOT, which are systemic or occur at a level deeper than topical oxygen can penetrate (see Hyperbaric Physics and Physiology section below). Topox is based on the concept that oxygen diffuses through tissue at a depth of 30-50 microns.³ This method does not treat DCS, arterial gas emboli (AGE), or carbon monoxide (CO) poisoning.  

Another problem with Topox is the design of the unit. A pressure differential must be created between the machine and open atmosphere to compress the machine. In order to keep the extremity from being pushed out of the pressurized machine, the cuff of the box must fit very tightly around the extremity, thereby creating a tourniquetlike effect. Topox is not covered by insurance, nor is it endorsed by the journal Diabetes Care for the treatment of foot ulcers.⁴

The other type of chamber is the portable "mild" hyperbaric chamber. These soft vessels can be pressurized to 1.5-1.7 atmospheres absolute (ATA). They are only approved by the FDA for the treatment of altitude illness. The number of these chambers has increased, as they are being used more commonly in off-label indications.

Hyperbaric Physics and Physiology

Physics of Hyperbaric Medicine

The physics behind hyperbaric oxygen therapy (HBOT) lies within the ideal gas laws.

• The application of Boyle’s law (p₁ v₁ = p₂ v₂) is seen in many aspects of HBOT. This can be useful with embolic phenomena such as decompression sickness (DCS) or arterial gas emboli (AGE). As the pressure is increased, the volume of the concerning bubble decreases. This also becomes important with chamber decompression; if a patient holds her breath, the volume of the gas trapped in the lungs overexpands and causes a pneumothorax.
• Charles’ law ([p₁ v₁]/T₁ = [p₂ v₂]/T₂) explains the temperature increase when the vessel is pressurized and the decrease in temperature with depressurization. This is important to remember when treating children or patients who are very sick or are intubated. 
• Henry’s law states that the amount of gas dissolved in a liquid is equal to the partial pressure of the gas exerted on the surface of the liquid. By increasing the atmospheric pressure in the chamber, more oxygen can be dissolved into the plasma than would be seen at surface pressure.

The clinician must be able to calculate how much oxygen a patient is receiving. In order to standardize this amount, atmospheres absolute (ATA) are used. This can be calculated from the percentage of oxygen in the gas mixture (usually 100% in HBOT; 21% if using air) and multiplied by the pressure. The pressure is expressed in feet of seawater (fsw), which is the pressure experienced if one were descending to that depth while in seawater. Depth and pressure can be measured in many ways; some common conversions are 1 atmosphere (atm) = 33 feet of seawater (fsw) = 10 meters of sea water (msw) = 14.7 pounds per square inch (psi) = 1.01 bar.

Hyperbaric Physiology

Table 1 below summarizes the physiologic mechanisms of HBOT. Each of these is discussed in the context of the indications for HBOT later in this article.

Table 1. Physiologic Mechanisms of Hyperbaric Oxygen Therapy

† Hyperoxia in normal tissues causes vasoconstriction, but this is compensated by increased plasma oxygen content and microvascular blood flow. This vasoconstrictive effect does, however, reduce posttraumatic tissue edema, which contributes to the treatment of crush injuries, compartment syndromes, and burns.

‡ HBOT increases the generation of oxygen free radicals, which oxidize proteins and membrane lipids, damage DNA, and inhibit bacterial metabolic functions. HBO is particularly effective against anaerobes and facilitates the oxygen-dependent peroxidase system by which leukocytes kill bacteria.

Additionally, evidence is growing that HBOT alters the levels of proinflammatory mediators and may blunt the inflammatory cascade. More studies are needed to further elucidate this complex interaction.

As HBOT is known to decrease heart rate while maintaining stroke volume, it has the potential to decrease cardiac output. At the same time, through systemic vasoconstriction, HBOT increases afterload. This combined effect can exacerbate congestive heart failure in patients with severe disease; however, clinically significant worsening of congestive heart failure is rare.

Contraindications

As with most medical treatments, absolute and relative contraindications exist with the use of hyperbaric oxygen therapy (HBOT).²

Table 2. Absolute Contraindications to Hyperbaric Oxygen Therapy

Decompression Sickness and Air Embolism

Decompression Sickness

• Type I involves musculoskeletal, skin, and lymphatic tissue, and often has accompanying fatigue.
• Type II includes neurologic systems (either CNS or peripheral), cardiorespiratory, audiovestibular, and shock.²⁵
• Type III DCS describes a syndrome that presents with symptoms that progress to a spinal deficit that may be refractory to recompression.

Air Embolism

Carbon Monoxide Poisoning

Carbon monoxide (CO) poisoning, whether intentional or accidental, occurs when one inhales the colorless and odorless carbon monoxide gas. Despite improved awareness and sensory alarms, multiple deaths occur each year.

CO binds to hemoglobin with 200 times the affinity of oxygen. CO also shifts the oxygen dissociation curve to the left (the Haldane effect), which decreases oxygen release to tissues. CO can also bind cytochrome oxidase aa3/C and myoglobin. Reperfusion injury can occur when free radicals and lipid peroxidation are produced.

The treatment of CO poisoning with hyperbaric oxygen therapy (HBOT) is based upon the theory that oxygen competitively displaces CO from hemoglobin. While breathing room air, this process takes about 300 minutes. While on a 100% oxygen nonrebreather mask, this time is reduced to about 90 minutes; with HBOT, the time is shortened to 32 minutes. HBOT (but not normobaric oxygen) restores cytochrome oxidase aa3/C³⁶ and helps to prevent lipid peroxidation.³⁷ HBOT is also used to help prevent the delayed neurologic sequelae (DNS); treatment instituted sooner is more effective.³⁸ Multiple papers describe controversial methods and conclusions about the use of HBOT for CO poisoning.^{39,37,40,41,42}

Patients with CO poisoning can present with myriad symptoms that they may not initially attribute to CO poisoning, as CO is considered the “great imitator” of other illnesses.^18,43,44 Presentation can include flulike symptoms such as headache, visual changes, dizziness, and nausea. More serious manifestations include loss of consciousness, seizures, chest pain, ECG changes, tachycardia, and mild to severe acidosis.

Candidates for HBOT are those who present with morbidity and mortality risks that include pregnancy and cardiovascular dysfunction and those who manifest signs of serious intoxication, such as unconsciousness (no matter how long a period), neurologic signs, or severe acidosis. CO-hemoglobin (Hgb) level usually does not correlate well with symptoms or outcome;^45,37,46 many patients with CO-Hgb levels of 25-30% are treated.

Pregnant females often have a CO level that is 10-15% lower than the fetus. Fetal Hgb not only has a higher affinity for CO but also has a left-shifted oxygen dissociation curve compared with adult hemoglobin. Exposure to CO causes an even farther leftward shift, in both adult and fetal hemoglobin, and decreased oxygen release from maternal blood to fetal blood and from fetal blood to fetal tissues. Pregnant patients with CO-Hgb levels greater than 10% should be treated with HBOT.²

HBOT is administered at 2.5-3 ATA for periods of 60-100 minutes. Depending on patient presentation and response, 1-5 treatments are recommended.³

Enhancement of Healing in Selected Problem Wounds

Normal wound healing proceeds through stages of hemostasis, removal of infectious agents, resolution of the inflammatory response, reestablishment of a connective tissue matrix, angiogenesis, and resurfacing. Problem (or chronic) wounds are those which do not proceed completely through this process because of any number of local and systemic host factors. For this reason, chronic wounds are often categorized as diabetic wounds, venous stasis ulcers, arterial ulcers, or pressure ulcers.

Wounds that fail to heal are typically hypoxic.⁴⁷ Multiple components of the wound healing process are affected by oxygen concentration or gradients, which explains why hyperbaric oxygen therapy (HBOT) can be an effective therapy to treat chronic wounds. Angiogenesis occurs in response to high oxygen concentration.¹⁰ This is likely a multifactorial effect of HBOT. First, fibroblast proliferation and collagen synthesis are oxygen dependent,¹¹ and collagen is the foundational matrix for angiogenesis. In addition, HBOT likely stimulates growth factors involving angiogenesis and other mediators of the wound healing process.⁴⁸ Hyperbaric oxygen also has been shown to have direct and indirect antimicrobial activity; in particular, it increases intracellular leukocyte killing.^13,14,12

Diabetic lower extremity ulcers have been the focus of most wound research in hyperbaric medicine, since the etiology of these wounds is multifactorial, and HBOT can address many of these factors. Several randomized controlled clinical trials have studied HBOT for the treatment of diabetic lower extremity wounds.^49,50,51,52 Additionally, many more prospective, noncontrolled clinical trials and retrospective trials have been completed. Based on the body of evidence, major insurance carriers around the world now endorse the use of HBOT for the treatment of diabetic lower extremity wounds that show evidence of deep soft tissue infection, osteomyelitis, or gangrene. HBOT has been shown to reduce the amputation rate in patients with diabetic ulcers as well.^49,50,52

In an effort to select patients appropriately for HBOT, various objective vascular evaluation methods have been used, including transcutaneous oximetry, capillary perfusion pressure, laser Doppler, and other types of vascular studies. Debate is ongoing regarding which method provides the most reliable data and whether these methods are more useful than other clinical markers of wound failure.

Note that HBOT should be used in conjunction with a complete wound healing care plan. As with all chronic wounds, other underlying host factors (eg, large vessel disease, glycemic control, nutrition, infection, presence of necrotic tissue, offloading) must be simultaneously addressed in order to have the highest chance of successful healing and functional capacity.

Because the goals of HBOT for wound healing include cellular proliferation and angiogenesis, HBOT is generally performed daily for a minimum of 30 treatments. Treatment is generally at 2 to 2.4 ATA for a total of 90 minutes of 100% oxygen breathing time. Based on the response to therapy, extended courses of therapy may be indicated.

Compromised Skin Grafts and Flaps

Most skin grafts and flaps in normal hosts heal well. In patients with compromised circulation, this may not be the case. Patients with diabetes or vasculopathy from another etiology and patients who have irradiated tissue are particularly subject to flap or graft compromise. In these patients, hyperbaric oxygen therapy (HBOT) has been shown to be useful. Unfortunately, if patients are not identified early, the initial flap or graft may be lost. Even in such cases, patients can significantly benefit from HBOT to prepare the wound bed for another graft or flap procedure; the procedure then has a higher chance of success following HBOT.

Over 30 animal studies have shown efficacy of HBOT in preserving both pedicled and free flaps in multiple models. These models looked at arterial, venous, and combined insults in addition to irradiated tissues. While improvement was observed regardless of the type of vascular defect, those with arterial insufficiency and radiation injury showed the greatest improvement.

Human case studies showing benefit of hyperbaric treatment for flap survival were first reported in 1966. A controlled clinical trial showing improved survival of split skin grafts followed shortly thereafter.⁵³ This was corroborated by a later clinical trial.⁵⁴ Additionally, evidence exists of benefit for flaps in post-irradiated tissue in human subjects.⁵⁵

As the underlying pathophysiology of all compromised grafts and flaps is hypoxia, HBOT benefits patients by reducing the oxygen deficit. A unique mechanism of action of HBOT for preserving compromised flaps is the possibility of closing arteriovenous shunts.⁵⁶ Additionally, the same mechanisms of action that improve wound healing, namely, improved fibroblast and collagen synthesis¹¹ and angiogenesis,¹⁰ also are likely to benefit a compromised graft or flap.

The current standard for HBOT to treat a compromised graft or flap includes twice daily treatment until the graft or flap appears viable and then once per day until completely healed. The initiation of HBOT should be expedited. In general, benefit should be seen by 20 treatments; if it is not, continuation of therapy should be reviewed. However, the cost of creating a complex flap is high, which makes HBOT cost-effective for this diagnosis. Of course, patients with compromised flaps need surgical attention to the arterial and venous supply, appropriate local management, and maximization of medical support.

Crush Injury and Compartment Syndrome

Acute peripheral traumatic ischemia includes those injuries that are caused by trauma that leads to ischemia and edema; a gradient of injury exists. This category contains crush injuries as well as compartment syndrome. Crush injuries often result in poor outcome because of the body’s attempt to manage the primary injury. The body then develops more injury due to the reperfusion response. Injuries are graded using definite points on a severity scale. The commonly referenced system is the Gustilo classification,⁵⁷ but other classification scales are available.

The benefits of hyperbaric oxygen therapy (HBOT) for this indication include hyperoxygenation by increasing oxygen within the plasma. HBOT also induces a reduction in blood flow^58,59 that allows capillaries to resorb extra fluid, resulting in decreased edema. As a gradient of oxygenation is based on blood flow, oxygen tissue tensions can be returned, allowing for the host defenses to properly function.¹¹ Animal studies suggest that a decreased neutrophil adherence to ischemic venules is observed with elevated oxygen pressures (2.5 ATA).^15,16 Reperfusion injury is diminished, as HBOT generates scavengers to destroy oxygen radicals.⁶⁰

Compartment syndrome also is a continuum of injury that occurs when compartment pressures exceed the capillary perfusion pressures. The extent to which the injury has affected tissues is unclear, even after surgical intervention.^61,58,62 HBOT is not recommended during the “suspected” stage of injury, when compartment syndrome is not yet present but may be impending. HBOT is beneficial during the impending stage, when objective signs are noted (pain, weakness, pain with passive stretch, tense compartment). With these signs, even if surgery is not elected because of compartment pressures or patient stability, HBOT is indicated. Once the patient has undergone fasciotomy, HBOT can be used to help decrease morbidity.³

HBOT should be started as soon as is feasible, ideally within 4-6 hours from time of injury. After emergent surgical intervention, the patient should undergo HBOT at 2-2.5 ATA for 60-90 minutes. For the next 2-3 days, perform HBOT 3 times daily, then twice daily for 2-3 days, and then daily for the next 2-3 days.²

Necrotizing Soft Tissue Infections

These infections may be single aerobic or anaerobic but are more often mixed infections that often occur as a result of trauma, surgical wounds, or foreign bodies, including subcutaneous and muscular injection of contaminated street drugs. They are often seen in compromised hosts who have diabetes or a vasculopathy of another type. These infections are named based on their clinical presentation and include necrotizing fasciitis, clostridial and nonclostridial myonecrosis, and Fournier gangrene.

Regardless of the depth of the tissue invasion, these infections have similar pathophysiology that includes local tissue hypoxia, which is exacerbated by a secondary occlusive endarteritis.⁶³ Intravascular sequestration of leukocytes is common in these types of infections, mediated by toxins from specific organisms.⁶⁴ Clostridial theta toxin appears to be one such mediator. All of these factors together foster an environment for facultative organisms to continue to consume remaining oxygen, and this promotes growth of anaerobes.

The cornerstones of therapy are wide surgical debridement and aggressive antibiotic therapy. Hyperbaric oxygen therapy (HBOT) is used adjunctively with these measures, as it offers several mechanisms of action to control the infection and reduce tissue loss. First, HBOT is toxic to anaerobic bacteria.⁶⁵ Next, HBOT improves polymorphonuclear function and bacterial clearance.^12,66 Based on results of work related to CO poisoning, HBOT may decrease neutrophil adherence based on inhibition of beta-2 integrin function.^17,16 Further investigation is needed to see if this mechanism is at work in necrotizing infections as well. In the case of clostridial myonecrosis, HBOT can stop the production of the alpha toxin.^19,67 Finally, limited evidence indicates that HBOT may facilitate antibiotic penetration or action in several classes of antibiotics, including aminoglycosides,²⁰ cephalosporins,²² sulfonamides²¹ and amphotericin.²³

Multiple clinical studies suggest that HBOT is efficacious in the treatment of necrotizing soft tissue infections. These include case series, retrospective and prospective studies, and non-randomized clinical trials. They suggest significant reductions in mortality and morbidity. The reduction in mortality was remarkably similar in 2 studies: 34% (untreated) vs. 11.9% (treated) in one study;⁶⁸ 38% (untreated) vs. 12.5% (treated) in the other.⁶⁹ In another study,⁷⁰ the treated group had more patients with diabetes and more patients in shock and still had significantly less mortality (23%) than the untreated group (66%). Clinical studies involving patients with Fournier gangrene treated with HBOT bear similar results.

Initial HBOT is aggressively performed at least twice per day in coordination with surgical debridement. Typically, a treatment pressure ranging from 2.0-2.5 ATA is adequate. However, in the specific case of clostridial myonecrosis, 3 ATA is often used to ensure adequate tissue oxygen tensions to stop alpha toxin production. For the same reason, HBOT should be initiated as quickly as possible in this circumstance and performed 3 times in the first 24 h if at all feasible.

Intracranial Abscess

Delayed Radiation Injury

Radiation therapy causes acute, subacute, and delayed injuries. Acute and subacute injuries are generally self-limited. However, delayed injuries are often much more difficult to treat and may appear anywhere from 6 months to years after treatment. They generally are seen after a minimum dose of 6000 cGy. While uncommon, these injuries can cause devastating chronic debilitation to patients. Notably, they can be quiescent until an invasive procedure is performed in the radiation field. Injuries are generally divided into soft tissue versus hard tissue injury (osteoradionecrosis [ORN]).

While the exact mechanism of delayed radiation injury is still being elucidated, the generally accepted explanation is that an obliterative endarteritis and tissue hypoxia lead to secondary fibrosis.⁷⁹ Hyperbaric oxygen therapy (HBOT) was first used to treat ORN of the mandible. Based on the foundational clinical research of Marx,⁸⁰ multiple subsequent studies supported its use. The success of HBOT in treating ORN then led to its use in soft tissue radionecrosis as well.

Osteoradionecrosis

Marx demonstrated conclusively that ORN is primarily an avascular aseptic necrosis rather than the result of infection.⁸⁰ He developed a staging system for classifying and planning treatment,⁸¹ which is largely accepted throughout the oromaxillofacial surgery community.

• Stage I - Exposed alveolar bone: The patient receives 30 HBOT treatments and then is reassessed for bone exposure, granulation, and resorption of nonviable bone. If response is favorable, an additional 10 treatments may be considered.
• Stage II - A patient who formerly was Stage I with incomplete response or failure to respond: Perform transoral sequestrectomy with primary wound closure followed by an additional 10 treatments.
• Stage III - A patient who fails stage II or has an orocutaneous fistula, pathologic fracture, or resorption to the inferior border of the mandible: The patient receives 30 treatments, transcutaneous mandibular resection, wound closure, and mandibular fixation, followed by an additional 10 postoperative treatments.
• Stage IIIR - Mandibular reconstruction 10 weeks after successful resolution of mandibular ORN: The patient receives 10 additional postoperative HBOT treatments.

The cornerstone of therapy is to begin and complete (if possible) HBOT prior to any surgical intervention and then to resume HBOT as soon as possible after surgery. Only in this way is adequate time allowed for angiogenesis to support postoperative healing. For patients with a history of significant radiation exposure, but no exposed bone, who require oral surgery, many practitioners suggest 20 HBOT treatments prior to surgery and 10 treatments immediately following surgery. Feldmeier has published an excellent review of this literature.⁸²

Soft Tissue Radionecrosis

While soft tissue radionecrosis also is rare, it causes significant morbidity, depending on the site of injury. All of these injuries lead to significant local pain. Both radiation cystitis and radiation proctitis can result in severe blood loss with symptomatic anemia, and radiation cystitis may cause obstructive uropathy secondary to fibrosis and blood clot formation. Radionecrosis of the neck and larynx can lead to dysphagia and respiratory obstruction. Irradiated skin develops painful, necrotic wounds that do not heal with standard wound healing care plans.

For each of these subpopulations of soft tissue radionecrosis, published case series and prospective, nonrandomized clinical trials corroborate one another, providing a degree of external validity. Larger studies are warranted. A national registry is currently being evaluated, from which more powerful conclusions may be forthcoming. Currently, the largest group of reported patients treated with HBOT for soft tissue radionecrosis are those with radiation cystitis. At least 15 publications, representing almost 200 patients, report a combined success rate in the 80% range. The 2 largest studies were published by Bevers⁸³ and Chong.⁸⁴

HBOT and Carcinogenesis

Practitioners and patients are often concerned that HBOT may foster recurrence of malignancy or promote the growth of an existing tumor. This is largely because of the known angiogenic effective of HBOT. Feldmeier has reviewed this subject extensively. Malignant angiogenesis appears to follow a different pathway than angiogenesis related to wound healing. His review of the literature suggests that the risk is low.⁸⁵

Refractory Osteomyelitis

Refractory osteomyelitis is defined as acute or chronic osteomyelitis that is not cured after appropriate interventions. More often than not, refractory osteomyelitis is seen in patients whose systems are compromised. This condition often results in nonhealing wounds, sinus tracts, and, in the worst case, more aggressive infections that require amputation.

Mader and Niinikoski showed that hyperbaric oxygen therapy (HBOT) is capable of elevating oxygen tension in infected bone to normal or above normal levels.^86,12 Since polymorphonuclear (PMN) function requires adequate oxygen concentration, this is a significant mechanism by which HBOT helps to control osteomyelitis, as demonstrated by Mader in the same study.¹²

A unique mechanism by which HBOT is beneficial in osteomyelitis is in promoting osteoclast function. The resorption of necrotic bone by osteoclasts is oxygen-dependent. This has best been demonstrated in animal models of osteomyelitis.⁸⁷

Additionally, as previously mentioned, HBOT facilitates the penetration or function of antibiotic drugs. Other properties of HBOT previously discussed, such as neovascularization and blunting the inflammatory response, likely provide additional benefit.

Convincing animal evidence supports the use of HBOT in the treatment of osteomyelitis. Clinical studies are somewhat problematic, however, because osteomyelitis has so many different presentations that comparisons become difficult. This is compounded by the small study sizes found in the literature; however, these do suggest benefit of HBOT for refractory osteomyelitis in humans.

One specific subset of osteomyelitis that merits special attention is malignant otitis externa. This progressive pseudomonal osteomyelitis of the ear canal can spread to the skull base and become fatal. Davis et al published a study of 17 patients with malignant otitis externa, all of whom showed dramatic improvement with the addition of HBOT to standard surgical debridement and antibiotic therapy.⁸⁸

Thermal Burns

Thermal burns present a multifactorial tissue injury that culminates in a marked inflammatory response with vascular derangement from activated platelets and white cell adhesion with resultant edema, hypoxia, and vulnerability to severe infection. Poor white cell function caused by the local environment exacerbates this problem. Hyperbaric oxygen therapy (HBOT) addresses each of these pathophysiological derangements, and can, therefore, make a significant difference in patient outcomes. These mechanisms of action have been discussed above.

Multiple animal studies support the utility of HBOT for treatment of thermal burns. Human studies ranging from case series to randomized clinical trials have supported the potential benefit of HBOT in burn treatment. These include a small randomized study by Hart⁸⁹ that demonstrated improved healing and decreased mortality. Niezgoda⁹⁰ showed increased healing in a standardized human burn model. In a series of publications, Cianci^91,92 suggests significant reduction in length of hospital stay, need for surgery, and cost.

Because of the goals of therapy, HBOT is begun as soon as possible after injury, with a goal of 3 treatments within the first 24 hours and then twice daily. Length of treatment depends on the clinical impairment of the patient and the extent of and response to grafting. Special attention must be given to fluid management and chamber and patient temperature to avoid undue physiologic stress to the patient as well as potential complications of treatment (ie, oxygen toxicity).

Exceptional Anemia

Patients who develop exceptional anemia have lost significant oxygen carrying capacity in the blood. These patients become candidates for hyperbaric oxygen therapy (HBOT) when they are unable to receive blood products because of religious or medical reasons. The major oxygen carrier in human blood is hemoglobin, transporting 1.34 mL of oxygen per gram. Borema performed an experiment in the 1960s in which exsanguinated pigs (who had only plasma in their vasculature) were able to sustain life under hyperbaric conditions.⁵

The body generally uses 5-6 vol% (mL of O₂ per 100 mL of blood);⁹³ under 3 ATA, 6 vol% of molecular oxygen can be dissolved into the plasma.⁹⁴ The CNS and cardiovascular systems are the two most oxygen-sensitive systems in the human body.^93,95 Oxygen debt is one way of determining a patient’s need to start or continue HBOT. A cumulative oxygen debt is the time integral of the volume of oxygen consumption (VO₂) measured during and after shock insult minus the baseline VO₂ required during the same time interval.³ Patients who have a debt >33 L/m² do not survive, whereas patients with debts ≤9 usually recover.²

HBOT is administered at 2-3 ATA for periods of up to 4 hours per treatment. As many as 3-4 sessions a day may be necessary, depending on a patient’s clinical picture. Treatments should continue until the patient can receive blood products, no longer demonstrates end stage organ failure, or no longer has a calculated oxygen debt.³

Complications and Special Concerns

As with any medical therapy, treatment brings both risks and benefits. One of the more frequently seen injuries caused by hyperbaric oxygen therapy (HBOT) is barotrauma (ie, injuries caused by pressure as a result of an inability to equalize pressure from an air-containing space and the surrounding environment).^2,3

Table 4. Complications to Hyperbaric Oxygen Therapy

Pediatric Considerations

Potential New Indications for Hyperbaric Oxygen Therapy

Central Retinal Vein Occlusion

Central retinal vein occlusion is a relatively common cause of visual loss. The main risk factors include diabetes, glaucoma, hypertension, and hypercoagulable conditions. Hyperbaric oxygen therapy (HBOT) provides oxygenation to the ischemic retina and diminishes retinal edema, allowing the retina to revascularize. The effect is sometimes rapid, and visual acuity may be significantly improved or nearly restored in a few treatments.

Multiple case reports, series, and retrospective analyses now show potential benefit.^96,97 Given the lack of other consistently efficacious treatments for this devastating condition, and the relative safety of HBOT, HBOT will likely be officially recommended for use by the Undersea and Hyperbaric Medical Society (UHMS) in late 2008.

Sudden Deafness

Bisphosphonate-Associated Osteonecrosis

Multimedia

Media file 1: Rectangular hyperbaric chamber.

Media file 2: Interior of rectangular chamber.

Media file 3: Cylindrical multiplace chamber.

Media file 4: Monoplace chamber.

References

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Keywords

hyperbaric oxygen, HBO, HBOT, oxygen therapy, hyperbaric oxygen chamber, HBO therapy, HBO treatment, hyperbaric medicine, hyperbaric therapy, diving medicine, decompression sickness, arterial gas embolism, diving accidents, radiation-damaged tissue, radionecrosis, osteoradionecrosis, radiation necrosis, soft tissue infections, necrotizing fasciitis, osteomyelitis, clostridial myonecrosis, non-healing wound, chronic wound, carbon monoxide poisoning, CO poisoning, compromised graft, compromised flap, crush injury, compartment syndrome, reperfusion injury

Contributor Information and Disclosures

Author

Emi Latham, MD, FACEP, Assistant Clinical Professor of Emergency and Hyperbaric Medicine, University of California at San Diego
Emi Latham, MD, FACEP is a member of the following medical societies: American College of Emergency Physicians and Undersea and Hyperbaric Medical Society
Disclosure: Nothing to disclose.

Coauthor(s)

Marc A Hare, MD, Assistant Clinical Professor of Medicine, Department of Emergency Medicine, University of California San Diego Medical Center; Medical Director, Center for Wound Healing and Hyperbaric Medicine, Paradise Valley Hospital
Marc A Hare, MD is a member of the following medical societies: American College of Emergency Physicians and Undersea and Hyperbaric Medical Society
Disclosure: Nothing to disclose.

Michael Neumeister, MD, FRCSC, FACS, Program Director, Assistant Professor, Department of Surgery, Division of Plastic Surgery, Southern Illinois University School of Medicine
Michael Neumeister, MD, FRCSC, FACS is a member of the following medical societies: American Academy of Dermatology, American Association for Hand Surgery, American Burn Association, American Medical Association, American Society of Plastic Surgeons, Canadian Medical Association, College of Physicians and Surgeons of Alberta, College of Physicians and Surgeons of Ontario, Pacific Dermatologic Association, Royal College of Physicians and Surgeons of Canada, and Undersea and Hyperbaric Medical Society
Disclosure: Nothing to disclose.

Medical Editor

Erik D Schraga, MD, Consulting Staff, Department of Emergency Medicine, Mills-Peninsula Emergency Medical Associates; Consulting Staff, Permanente Medical Group, Kaiser Permanente, Santa Clara Medical Center
Disclosure: Nothing to disclose.

Pharmacy Editor

Mary L Windle, PharmD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy, Pharmacy Editor, eMedicine
Disclosure: Pfizer Inc Stock Investment from broker recommendation; Avanir Pharma Stock Investment from broker recommendation

Chief Editor

Rick Kulkarni, MD, Medical Director, Assistant Professor of Surgery, Section of Emergency Medicine, Yale-New Haven Hospital
Rick Kulkarni, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Emergency Medicine, American College of Emergency Physicians, American Medical Association, American Medical Informatics Association, Phi Beta Kappa, and Society for Academic Emergency Medicine
Disclosure: WebMD Salary Employment

Multiplace hyperbaric chamber photos courtesy of OxyHeal Health Group, Inc.

Monoplace hyperbaric chamber photos courtesy of Sechrist Industries, Inc.

Jain KK, Neubauer RA. Textbook of Hyperbaric Medicine. 4th ed., revised. Seattle, Wash: Hogrefe and Huber Publishing; 2004.

Neuman T, Thom S, eds. Physiology and Medicine of Hyperbaric Oxygen Therapy. Philadelphia, Pa: Saunders/Elsevier; 2008.

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